The present invention relates to grates for furnaces, especially for industrial furnaces, and more particularly to improvements in grate bars for use in composite grates of such furnaces.
It is already known to assemble the grate of an industrial furnace from discrete grate bars which are supported by a frame and serve to support solid fuel while permitting streams of preheated air to penetrate therebetween and to rise into contact with the fuel. Reference may be had to German Pat. No. 28 06 974. This patent discloses grate bars of the type wherein a longitudinally extending top wall is integrally connected with downwardly extending longitudinal sidewalls, a front wall and a rear wall. The grate bars which are disclosed in the German patent further comprise a bottom wall which is spaced apart from the top wall and defines with the remaining walls an air heating chamber wherein the inflowing fresh air is preheated preparatory to admission into the combustion chamber of the furnace. The underside of the top wall is provided with downwardly extending cooling ribs which divide the air heating chamber into longitudinally extending channels wherein fresh air can flow from a first opening at the rear wall toward a second opening in one of the sidewalls close to the front wall. It is also known to provide in front of the ribs a compartment which receives fresh air from the channels and communicates with the second opening in the one sidewall.
The grate bar which is disclosed in the German patent has a small number of ribs so that such ribs define rather wide channels for the flow of fresh air from the first opening toward the compartment behind the front wall. This is considered desirable and advantageous because any solid particles which descend from the combustion chamber and enter the compartment by way of the second opening can readily leave the air heating chamber by advancing along the bottom wall rearwardly toward and by leaving the grate bar by way of the first opening. When the grate bar is installed in the furnace, the bottom wall slopes rearwardly and downwardly so that any solid particles which enter the air heating chamber exhibit a tendency to advance along the downwardly sloping upper side of the bottom wall and to leave the grate bar via the first opening. However, the air heating action of such grate bars is rather limited in view of the relatively small number of cooling ribs in the air heating chamber, i.e., the exchange of heat between the inflowing fresh air and the ribs is not very pronounced so that the temperature of air leaving the grate bar via the second opening is too low. Moreover, the relatively small number of ribs cannot ensure adequate cooling of the grate bar. On the other hand, the number of ribs in such conventional grate bars cannot be increased at will because this results in undue narrowing of the channels and renders it likely that the channels become clogged with solid particles to thus prevent the admission of requisite quantities of fresh air and adequate cooling of the grate bar.